This invention relates to optical-to-electrical and electrical-to-optical modules.
More particularly, the present invention relates to optical alignment features in such modules.
In optical-to-electrical and electrical-to-optical (hereinafter xe2x80x9coptoelectricxe2x80x9d) modules used in the various communications fields, one of the most difficult problems that must be solved is the efficient transmission of light between a light. generating device and an optical fiber or, alternatively, the transmission of light from the optical fiber to a light receiving device. Here it will be understood by those skilled in the art that the term xe2x80x9clightxe2x80x9d is a generic term which includes any electromagnetic radiation that can be modulated and transmitted by optical fibers or other optical transmission lines. Because optical fibers and the active regions of light generating devices and light receiving devices are very small, alignment of an optical fiber with a light generating device or a light receiving device is difficult and can be very work intensive and time consuming.
For example, one method used to align an optical fiber with a light generating device or a light receiving device is called active alignment. In this process a light is introduced at one end of the optical fiber and the other end is moved adjacent the active area of an operative light receiving device, while monitoring the output of the light receiving device, until a maximum output signal is received. Alternatively, an operative light receiving device is attached to one end of an optical fiber and the other end is moved adjacent the active area of an operative light generating device until a maximum output signal is received. In both instances the amount of time and effort required to obtain the optimum alignment is extensive.
In a perfect system, all of the light generated passes directly into an optical fiber and all of the light exiting an optical fiber is directed onto an active surface of a light receiving device. However, in the real world much of the generated light travels outwardly in a direction to miss the optical fiber and some of the light impinging on the optical fiber is reflected back into the light generating device. Much of the cause of this outwardly or misdirected light comes from poor alignment along the Z axis (the axis of light propagation) as well as misalignment in the X and Y axes (defining a plane perpendicular to the direction of light propagation). The outwardly or misdirected light can impinge on adjacent devices to produce unwanted cross-talk within the system. Also, the reflected light can be directed back into the light generating device or the optical fiber and can interfere with generated light to produce unwanted and troublesome modes or frequencies. Also, the loss of light through misdirection and/or reflection means that additional power must be used to produce sufficient light to transmit between various devices, thus reducing efficiency.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object the present invention to provide new and improved optical alignment features.
Another object of the present invention is to provide new and improved optical alignment features which reduce time and effort in alignment procedures.
And another object of the present invention is to provide new and improved optical alignment features which improve the efficiency of optical systems.
Still another object of the present invention is to provide new and improved optical alignment features which allow the use of a variety of components and component materials.
Briefly, to achieve the desired objects of the present invention in accordance with a preferred embodiment thereof, provided is optical alignment apparatus which includes a first element mounting a first lens and a light source and a second element mounting a second lens and a light receiving structure. The first lens is placed a first distance from the light source and is constructed to collimate light received from the light source. The first and second elements are mounted relative to each other to position the second lens a third distance from the first lens and to receive the collimated light from the first lens. The second lens is positioned a second distance from the light receiving structure to focus the collimated light on the light receiving structure. The first and second lens are constructed so that the first and second distances are dependent upon each other and the third distance is independent of the first and second distances.
In general, the light source is one of a laser, a light emitting diode, a light communicating optical fiber, or any other source of light for communication and the light receiving structure is any device that converts light energy into electrical energy, such as a photo-diode, a PIN diode, or one end of a light communicating optical fiber having such a: device positioned at the other end. The lens are constructed and positioned so that the first distance between the light source and the first lens determines a major portion of the optical power of the apparatus, so that the second lens can be formed of a low tolerance molded plastic part. Also, in some embodiments one of the first and second lenses can be formed to direct, impinging light received along a first axis, at an angle to the first axis and may include, for example, a curved reflecting surface.